Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, Australia.
School of Medicine, Western Sydney University, Campbelltown, NSW, Australia.
Oecologia. 2021 May;196(1):145-154. doi: 10.1007/s00442-021-04902-1. Epub 2021 Apr 30.
Grasses accumulate large amounts of silicon (Si) which acts as a highly effective physical defence against insect herbivory, however recent evidence shows that Si supplementation also modifies plant secondary metabolite concetrations. Changes in plant secondary metabolites concentrations can have cascading effects on higher trophic levels, such as parasitoids, as they are dependent on the host herbivore for growth and development. However, relatively little is known about how Si application affects higher trophic levels. We examined the effects of Si addition on alkaloid content in leaves of Phalaris aquatica (Poaceae) and the effect on interactions between an aphid (Rhopalosiphum padi) and its parasitoid (Aphidius colemani). Si supplementation had no effect on aphid abundance or parasitism rate. Adult aphids, aphid mummies (parasitised aphids) and the emergent parasitoids were, however, significantly smaller on Si+ plants. Parasitoid traits (size and emergence) were correlated with aphid mummy size. Si addition reduced parasitoid emergence rate and size due to reduced host mummy size, in addition, significantly fewer females emerged from mummies on Si+ plants. Aphid infestation significantly altered alkaloids concentrations, reducing gramine by 80% while increasing tryptamine by 91% in Si- plants. Si addition reduced aphid-induced tryptamine concentrations by 64% and increased 5-MeO-tryptamine by over 800% in control and 142% in aphid infested plants. Our results show that while Si addition has modest impacts on the herbivore, it significantly alters secondary metabolites and has stronger effects on the higher trophic level through changes in the quality of the parasitised host.
草类植物会积累大量的硅（Si），硅能起到抵御昆虫食草的高效物理防御作用，然而最近的证据表明，硅补充剂也会改变植物次生代谢物的浓度。植物次生代谢物浓度的变化会对更高营养级产生级联效应，例如寄生蜂，因为它们的生长和发育依赖于宿主食草动物。然而，人们对硅的应用如何影响更高营养级知之甚少。我们研究了硅添加对水生雀麦（禾本科）叶片生物碱含量的影响，以及对蚜虫（黑尾叶蝉）及其寄生蜂（麦蚜茧蜂）之间相互作用的影响。硅补充对蚜虫的丰度或寄生率没有影响。然而，在 Si+植物上，成虫蚜虫、蚜虫蛹（被寄生的蚜虫）和新出现的寄生蜂明显更小。寄生蜂的特征（大小和出现）与蚜虫蛹的大小相关。由于寄主蛹的大小减小，硅的添加降低了寄生蜂的出现率和大小，此外，在 Si+植物上从蛹中出现的雌性数量明显减少。蚜虫的侵扰显著改变了生物碱的浓度，使 Si- 植物中的禾草碱减少 80%，而色胺增加 91%。硅的添加降低了蚜虫诱导的色胺浓度，在对照植物中降低了 64%，在受蚜虫侵扰的植物中增加了 800%以上，在受蚜虫侵扰的植物中增加了 142%。我们的结果表明，虽然硅的添加对食草动物有适度的影响，但它通过改变被寄生宿主的质量，显著改变次生代谢物，并对更高营养级产生更强的影响。
